Optical fibres as sensors:-
Generally, optic sensor consists of light source, optical fibres and detector. The sensors are Two types active sensors and passive sensors. The physical changes directly changes the electrical responses called active sensors; where as the physical changes are indirectly recorded to sensing is called passive sensors.
Temperature sensor:-
The light can be arranged to fall on reflecting surface and the associated phase angle is be measured. The reflecting surface can be varied using temperature variation, which causes additional phase angle to light wave as seen in the figure When light thrown on the reflector by optical fibre, the initial and final response can be compared for measure of temperature by relative correlation.
Displacement sensors:-
The light is sent through transmitting fibre and further it is allowed to fall on moving target. The light ray falls on the surface and gets reflected. The incident ray could mix with reflected wave and forms standing wave to which the phase angle shift can be measured. The below figure indicates displacement sensors.
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